Aluminum alloy powders for powder bed fusion additive manufacturing processes

ABSTRACT

A three-dimensional aluminum alloy part may be manufactured by a process in which a layer of aluminum alloy powder feed material is distributed over a substrate and scanned with a high-energy laser or electron beam in selective regions corresponding to a cross-section of the aluminum alloy part being formed. During the manufacturing process, the selective regions may melt and form a pool of molten aluminum alloy material. Thereafter, the pool of molten aluminum alloy material may cool and solidify into a solid layer of fused aluminum alloy material. During solidification of the pool of molten aluminum alloy material, solid phase particles may form within a solution of liquid phase aluminum prior to formation of solid phase aluminum dendrites. The resulting aluminum alloy part may exhibit a polycrystalline structure that predominantly includes a plurality of equiaxed grains, instead of columnar grains.

INTRODUCTION

A variety of aluminum alloy compositions have been developed for use in the manufacture of three-dimensional aluminum alloy parts via casting and/or hot forming operations to impart certain desirable chemical and mechanical properties to the resulting parts. However, it has been found that when such aluminum alloy compositions are employed as a powder feed material in a powder bed fusion additive manufacturing process, the resulting aluminum alloy parts oftentimes exhibit a columnar grain structure, and thus are relatively susceptible to cracking along grain boundaries between adjacent columnar grains. Therefore, there is a need in the art for an aluminum alloy composition that can be employed in a powder bed fusion additive manufacturing process to form three-dimensional aluminum alloy parts that predominantly exhibit an equiaxed grain structure and thus are relatively resistant or impervious to solidification cracking.

SUMMARY

In accordance with one aspect of the present disclosure, an aluminum alloy powder for manufacturing a three-dimensional high-strength aluminum alloy part by a powder bed fusion additive manufacturing process is provided. Each particle of the aluminum alloy powder may comprise an aluminum alloy that includes, by weight, 13-25% silicon, 0.1-10% copper, and 0-2% magnesium. When the aluminum alloy is heated to a first temperature greater than a liquidus temperature of the aluminum alloy and subsequently cooled to a second temperature less than the liquidus temperature of the aluminum alloy and greater than a solidus temperature of the aluminum alloy, the aluminum alloy may transition from a liquid phase to a multiphase system. The multiphase system may include a solution of liquid phase aluminum and a solid phase of silicon particles dispersed throughout the liquid phase aluminum.

In one form, the aluminum alloy may comprise, by weight, 15-22% silicon, 2-5.1% copper, and 0.6-0.8% magnesium. In another form, the aluminum alloy powder may comprise, by weight, 19-21% silicon, 3.5-4.1% copper, and aluminum as balance.

The aluminum also may comprise, by weight: greater than 0% iron and less than 9% iron, and greater than 0% manganese and less than 5% manganese. In such case, the multiphase system may include the solution of liquid phase aluminum, the solid phase of silicon particles, and another solid phase of iron-containing intermetallic particles dispersed throughout the liquid phase aluminum.

In accordance with another aspect of the present disclosure, an aluminum alloy powder for manufacturing a three-dimensional high thermal conductivity aluminum alloy part by a powder bed fusion additive manufacturing process is provided. Each particle of the aluminum alloy powder may comprise an aluminum alloy that includes, by weight: greater than 95% aluminum, and greater than 0% and less than 5% of at least one nucleating agent. The at least one nucleating agent may comprise an element or compound having a solid solubility in aluminum of, by weight, less than 0.5% at temperatures less than 530 degrees Celsius. When the aluminum alloy is heated to a first temperature greater than a liquidus temperature of the aluminum alloy and subsequently cooled to a second temperature less than the liquidus temperature of the aluminum alloy and greater than a solidus temperature of the aluminum alloy, the aluminum alloy may transition from a liquid phase to a multiphase system. The multiphase system may include a solution of liquid phase aluminum and a solid phase of particles of the at least one nucleating agent dispersed throughout the liquid phase aluminum. In one form, the at least one nucleating agent may comprise an element or compound having a solid solubility in aluminum of, by weight, less than or equal to 2.0% at the second temperature.

A method of manufacturing a three-dimensional aluminum alloy part may comprise the following step. In step (a), an aluminum alloy powder feed material may be provided. In step (b), a layer of the powder feed material may be distributed over a substrate. In step (c), selective regions of the layer of the powder feed material may be scanned with a high-energy laser or electron beam to form a pool of molten aluminum alloy material therein. The selective regions of the layer of the powder feed material may correspond to a cross-section of an aluminum alloy part being formed. In step (d), the laser or electron beam may be terminated to cool and solidify the pool of molten aluminum alloy material into a solid layer of fused aluminum alloy material. Steps (b) through (d) may be sequentially repeated to form an aluminum alloy part made up of a plurality of solid layers of fused aluminum alloy material. During solidification of the pool of molten aluminum alloy material, solid phase particles may form within a solution of liquid phase aluminum prior to formation of solid phase aluminum dendrites. Each of the solid layers of fused aluminum alloy material in the aluminum alloy part may include a continuous aluminum matrix phase that exhibits a polycrystalline structure and predominantly includes a plurality of equiaxed grains.

After termination of the laser or electron beam, the pool of molten aluminum alloy material may be cooled at a rate in the range of 10⁴ Kelvin per second to 10⁶ Kelvin per second.

During solidification of the pool of molten aluminum alloy material, the molten aluminum alloy material may transition from an entirely liquid phase to a multiphase system. In the multiphase system, the solid phase particles may be dispersed throughout the solution of liquid phase aluminum.

The solid phase particles may serve as nuclei for the subsequent formation of the solid phase aluminum dendrites. In such case, after the solid phase particles form within the solution of liquid phase aluminum, the solid phase aluminum dendrites may nucleate and grow in multiple directions on the solid phase particles. Growth of the solid phase aluminum dendrites may be arrested when neighboring aluminum dendrites impinge upon one another and form grain boundaries.

In one form, each particle of the aluminum alloy powder feed material may comprise, by weight, 13-25% silicon. In such case, the solid phase particles may comprise particles of silicon.

Each particle of the aluminum alloy powder feed material also may comprise, by weight: greater than 0% iron and less than 9% iron, and greater than 0% manganese and less than 5% manganese. In such case, the solid phase particles may comprise the particles of silicon and iron-containing intermetallic particles.

Each particle of the aluminum alloy powder feed material also may comprise, by weight, 0.1-10% copper and 0-2% magnesium. In such case, the aluminum alloy part may be heated at a temperature in the range of 180° C. to 210° C. for a duration of 0.5 hours to 7 hours to form at least one copper-containing precipitate phase within the aluminum matrix phase of each of the solid layers of fused aluminum alloy material in the aluminum alloy part.

In another form, each particle of the aluminum alloy powder feed material may comprise, by weight: greater than 95% aluminum, and greater than 0% and less than 5% of at least one nucleating agent. The at least one nucleating agent may comprise an element or compound having a solid solubility in aluminum of, by weight, less than 0.5% at temperatures less than 530 degrees Celsius.

In one specific example, each particle of the aluminum alloy powder feed material may comprise, by weight, greater than 98% aluminum and less than 2% of the at least one nucleating agent.

The at least one nucleating agent may comprise at least one element or compound of titanium (Ti), boron (B), beryllium (Be), cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), hafnium (Hf), manganese (Mn), molybdenum (Mo), niobium (Nb), lead (Pb), sulfur (S), zirconium (Zr), antimony (Sb), scandium (Sc), selenium (Se), strontium (Sr), tantalum (Ta), vanadium (V), or tungsten (W).

In one form, each particle of the aluminum alloy powder feed material may comprise, by weight, at least one of greater than 0% B and less than 5% B, greater than or equal to 0.7% Be and less than 5% Be, greater than or equal to 0.9% Co and less than 5% Co, greater than or equal to 0.3% Cr and less than 5% Cr, greater than 0% Cs and less than 5% Cs, greater than or equal to 1.7% Fe and less than 5% Fe, greater than or equal to 0.4% Hf and less than 5% Hf, greater than or equal to 1.8% Mn and less than 5% Mn, greater than 0% Mo and less than 5% Mo, greater than 0% Nb and less than 5% Nb, greater than or equal to 1.4% Pb and less than 5% Pb, greater than 0% S and less than 5% S, greater than or equal to 0.9% Sb and less than 5% Sb, greater than or equal to 0.4% Sc and less than 5% Sc, greater than 0% Se and less than 5% Se, greater than or equal to 0.5% Sr and less than 5% Sr, greater than 0% Ta and less than 5% Ta, greater than or equal to 0.12% Ti and less than 5% Ti, greater than 0% V and less than 5% V, greater than 0% W and less than 5% W, or greater than 0% Zr and less than 5% Zr.

In one specific form, each particle of the aluminum alloy powder feed material may comprise, by weight, greater than 0.12% Ti, less than 5% Ti, and aluminum as balance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a temperature (° C.) vs. composition equilibrium phase diagram of a binary Al—Si alloy system;

FIG. 2 is a schematic perspective view of an apparatus for manufacturing aluminum alloy parts via a powder bed fusion additive manufacturing process using an aluminum alloy powder feed material, in accordance with one embodiment of the present disclosure;

FIG. 3 is a magnified view of a layer of the aluminum alloy powder feed material distributed over a previously solidified layer of aluminum alloy material on a building platform of the apparatus of FIG. 2;

FIG. 4 is a magnified view of a laser beam impinging upon and melting the layer of the aluminum alloy powder feed material of FIG. 3;

FIG. 5 is a schematic illustration of a plurality of columnar-shaped aluminum dendrites growing in epitaxy with a surface of a substrate during solidification of a conventional aluminum alloy;

FIG. 6 is a schematic illustration of a plurality of unidirectionally solidified columnar grains formed within the conventional aluminum alloy of FIG. 5 after solidification thereof;

FIG. 7 is a schematic illustration of a plurality of solid phase particles serving as nuclei for the subsequent nucleation and growth of aluminum dendrites during solidification of the presently disclosed aluminum alloys; and

FIG. 8 is a schematic illustration of a plurality of equiaxed grains formed within the aluminum alloy of FIG. 7 after solidification thereof.

DETAILED DESCRIPTION

The presently disclosed aluminum alloys can be prepared in powder form and used in various powder bed fusion additive manufacturing processes to produce three-dimensional aluminum alloy parts that predominantly exhibit an equiaxed grain structure and relatively high resistance to solidification cracking, as compared to aluminum alloy parts that predominantly exhibit a columnar grain structure. To inhibit the formation of columnar grains within the aluminum alloy parts during the powder bed fusion process, the aluminum alloys include at least one element or compound that, during solidification of the aluminum alloys, nucleates within a solution of liquid phase aluminum and serves as nuclei for the subsequent nucleation and growth of aluminum dendrites. As the aluminum dendrites grow outward in all directions from their respective nuclei, the aluminum dendrites eventually impinge upon neighboring dendrites and form grain boundaries. Because the nucleation and growth of the aluminum dendrites occurs throughout the solidifying aluminum alloy, instead of along a single plane (e.g., on a substrate or on a layer of previously solidified aluminum alloy material), the formation of columnar grains within the solidifying alloy is prevented or inhibited.

As used herein, the term “aluminum alloy” refers to a material that comprises, by weight, greater than or equal to 50% aluminum (Al) and one or more other elements selected to impart certain desirable properties to the material that are not exhibited by pure aluminum.

In one form, an aluminum alloy composition for manufacturing a three-dimensional high-strength aluminum alloy part by an additive manufacturing process may comprise, in addition to aluminum, alloying elements of silicon (Si) and copper (Cu), and thus may be referred to herein as an “Al—Si—Cu alloy.” More specifically, the Al—Si—Cu alloy may comprise, by weight, greater than or equal to 13%, 15%, or 19% silicon; less than 25%, 22%, or 21% silicon; or between 13-25%, 15-22%, or 19-21% silicon. In addition, the Al—Si—Cu alloy may comprise, by weight, greater than or equal to 0.1%, 2%, or 3.5% copper; less than 10%, 5.1%, or 4.1%, copper; or between 0.1-10%, 2-5.1%, or 3.5-4.1% copper.

FIG. 1 depicts an equilibrium phase diagram 10 for a binary Al—Si alloy. As shown, a binary Al—Si alloy that includes, by weight, about 12.6% Si and the balance Al is a eutectic composition, as indicated by the presence of a eutectic-type invariant point 12 at such composition on the binary Al—Si equilibrium phase diagram 10. At the eutectic point 12, the liquidus lines 14 and the solidus line 16 intersect and, at equilibrium, a liquid phase (L) and two solid phases, i.e., Al_((s)) and solid Si_((s)), coexist. Binary Al—Si alloys that include, by weight, greater than 12.6% Si and the balance Al (such as the presently disclosed Al—Si—Cu alloy) contain more Si than the Al—Si eutectic composition and thus are referred to as hypereutectic compositions. As shown in FIG. 1, when a binary Al—Si alloy having a eutectic composition is cooled through the eutectic point 12, from a first temperature above the solidus line 16 (and above the eutectic temperature (T_(E)) of the alloy (i.e., about 577° C.)) to a second temperature below the solidus line 16 and below the T_(E) of the alloy, the Al—Si alloy undergoes a eutectic transformation and transitions from an entirely liquid phase (L) to an entirely solid phase (Al_((s))+Si_((s))). On the other hand, when an Al—Si alloy having a hypereutectic composition is melted to form an entirely liquid phase (L) and is subsequently cooled from a first temperature above the liquidus line 14 to a second temperature below the liquidus line 14, the Al—Si alloy does not directly transition from the liquid phase (L) to an entirely solid phase. Instead, as this hypereutectic Al—Si alloy is cooled to a temperature below the liquidus line 14, the Al—Si alloy transitions to a two-phase system, including a liquid phase (L) of aluminum and a solid phase (Si_((s))) of substantially pure silicon particles. If the hypereutectic Al—Si alloy is further cooled to a third temperature below the solidus line 16, the Al—Si alloy will eventually transition to an entirely solid phase including an aluminum matrix phase and a dispersed phase of silicon (Al_((s))+Si_((s))). Without intending to be bound by theory, it is believed that the solidification behavior of a binary Al—Si alloy having a eutectic or hypereutectic composition may be due, at least in part, to the exceptionally low solubility of silicon in aluminum and the relatively high melting point of silicon (m.p.˜1414° C.) as compared to that of aluminum (m.p.˜660° C.).

The amount of silicon in the Al—Si—Cu alloy described herein is selected so that the Al—Si—Cu alloy exhibits a hypereutectic composition and can be heated to a temperature above a liquidus temperature of the Al—Si—Cu alloy and subsequently cooled to a temperature below a solidus temperature of the Al—Si—Cu alloy to produce an entirely solid polycrystalline Al—Si—Cu alloy that predominantly exhibits an equiaxed grain structure, instead of a columnar grain structure. Without intending to be bound by theory, it is believed that the equiaxed grain structure of the resulting polycrystalline Al—Si—Cu alloy is due, at least in part, to the solidification behavior of the Al—Si—Cu alloy. In particular, it is believed that, when the hypereutectic Al—Si—Cu alloy is heated to a temperature above the liquidus temperature of the Al—Si—Cu alloy and subsequently cooled to a temperature below the liquidus temperature of the Al—Si—Cu alloy, the Al—Si—Cu alloy will transition from an entirely liquid phase to a multiphase system. During this transition, particles of solid phase silicon will nucleate throughout a solution of liquid phase aluminum to produce a multiphase system that includes a solution of liquid phase aluminum and a solid phase of silicon particles dispersed throughout the liquid phase aluminum. Nucleation of the particles of solid phase silicon may occur simultaneously throughout multiple horizontally and vertically spaced-apart regions of the solution of liquid phase aluminum, and may occur generally homogeneously throughout the solution of liquid phase aluminum. Thereafter, when the hypereutectic Al—Si—Cu alloy is further cooled to a temperature at or below the solidus temperature of the Al—Si—Cu alloy, solid phase aluminum dendrites will nucleate and grow in multiple directions on the previously formed silicon particles. Growth of these aluminum dendrites will eventually be arrested when neighboring aluminum dendrites impinge upon one another and form grain boundaries. After the hypereutectic Al—Si—Cu alloy has completely solidified, the Al—Si—Cu alloy will exhibit a polycrystalline structure including a continuous aluminum matrix phase and a dispersed phase of silicon. In addition, the resulting hypereutectic Al—Si—Cu alloy will predominantly include a plurality of randomly oriented equiaxed grains, instead of columnar grains. The equiaxed grains may have a mean grain diameter in the range of 0.1 μm to 50 μm.

The Al—Si—Cu alloy may have a liquidus temperature in the range of 570° C. to 850° C., and a solidus temperature in the range of 500° C. to 540° C. As such, the Al—Si—Cu alloy may exhibit a multiphase system of liquid phase aluminum and solid phase silicon at a temperature in the range of 500° C. to 850° C.

As used herein, the term “predominantly” means something, for example, a grain structure, that is present in the greatest amount by volume, as compared to other similar things, for example, as compared to other grain structures.

The amount of copper in the Al—Si—Cu alloy is selected to provide the alloy with the ability to develop one or more Cu-containing precipitate phases within the aluminum matrix phase when the Al—Si—Cu alloy is subjected to a heat treatment process. For example, the amount of copper in the Al—Si—Cu alloy may be selected to provide the alloy with the ability to develop an Al- and Cu-based precipitate (referred to herein as an “AlCu precipitate”) phase within the aluminum matrix phase when the Al—Si—Cu alloy is subjected to a heat treatment process that includes an aging heat treatment stage and optionally a solution heat treatment stage. The AlCu precipitate phase is Al- and Cu-based, meaning that Al and Cu constitute the largest constituents of the precipitate phase by weight. Formation of the AlCu precipitate phase within the aluminum matrix phase may provide the Al—Si—Cu alloy with high strength at relatively low temperatures, e.g., at ambient temperature (e.g., 25° C.) and at temperatures up to about 200° C.

In some embodiments, the Al—Si—Cu alloy also may comprise alloying elements of magnesium (Mg), iron (Fe), and/or manganese (Mn). When present, the Al—Si—Cu alloy may comprise, by weight, greater than or equal to 0%, 0.5%, or 0.6% magnesium; less than 2%, 1.5%, or 0.8% magnesium; or between 0-2%, 0.5-1.5%, or 0.6-0.8% magnesium. The Al—Si—Cu alloy may comprise, by weight, greater than or equal to 0% or 7% iron; less than 10% or 9% iron; or between 0-10% or 7-9% iron. The Al—Si—Cu alloy may comprise, by weight, greater than or equal to 0% or 3% manganese; less than 6% or 5% manganese; or between 0-6% or 3-5% manganese.

The amount of magnesium in the Al—Si—Cu alloy may be selected to provide the alloy with the ability to develop an Al-, Cu-, Mg-, and Si-based precipitate (referred to herein as an “AlCuMgSi precipitate”) phase within the aluminum matrix phase when the Al—Si—Cu alloy is subjected to a heat treatment process that includes an aging heat treatment stage and optionally a solution heat treatment stage. The AlCuMgSi precipitate phase is Al-, Cu-, Mg-, and Si-based, meaning that Al, Cu, Mg, and Si constitute the largest constituents of the precipitate phase by weight. Formation of the AlCuMgSi precipitate phase within the aluminum matrix phase may provide the Al—Si—Cu alloy with high strength at ambient temperature and at elevated temperatures (e.g., up to about 300° C.).

The amount of iron and manganese in the Al—Si—Cu alloy may be selected to promote the formation of at least one intermetallic phase within the Al—Si—Cu alloy during solidification thereof. In particular, the amount of iron and/or manganese in the Al—Si—Cu alloy may be selected so that at least one intermetallic phase nucleates within the liquid phase aluminum during solidification of the Al—Si—Cu alloy and provides additional nucleation sites (in addition to the nucleation sites provided by the silicon particles) for the subsequent nucleation and equiaxed growth of aluminum dendrites. For example, the at least one intermetallic phase may comprise an Fe-containing intermetallic phase and/or a Mn-containing intermetallic phase. In one specific example, the amount of iron in the Al—Si—Cu alloy may be selected to promote the formation of solid particles of an Al-, Fe-, and Si-based intermetallic (referred to herein as an “AlFeSi intermetallic”) phase within the liquid phase aluminum during solidification of the Al—Si—Cu alloy. The AlFeSi intermetallic phase is Al-, Fe-, and Si-based, meaning that Al, Fe, and Si are the largest constituents of the intermetallic phase. For example, the combined amounts of Al, Fe, and Si in the AlFeSi intermetallic phase may account for, by weight, greater than 50% of the AlFeSi intermetallic phase and, in some cases, greater than 90% of the AlFeSi intermetallic phase.

In embodiments where the Al—Si—Cu alloy comprises iron, the amount of manganese in the Al—Si—Cu alloy may be selected to promote the formation of an Al-, Fe-, Mn-, and Si-based intermetallic (referred to herein as an “AlFeMnSi intermetallic”) phase within the liquid phase aluminum during solidification of the Al—Si—Cu alloy and to inhibit the formation of an Al-, Fe-, and Si-based intermetallic (referred to herein as an “AlFeSi intermetallic”) phase.

The hypereutectic Al—Si—Cu alloy does not require addition of scandium (Sc) to achieve an equiaxed grain structure during solidification thereof. As such, the amount of Sc in the Al—Si—Cu alloy may be less than 0.2%, preferably less than 0.05%, and more preferably less than 0.01% by weight of the Al—Si—Cu alloy.

Additional elements not intentionally introduced into the composition of the Al—Si—Cu alloy nonetheless may be inherently present in the alloy in relatively small amounts, for example, less than 0.2%, preferably less than 0.05%, and more preferably less than 0.01% by weight of the Al—Si—Cu alloy. Such elements may be present, for example, as impurities in the raw materials used to prepare the Al—Si—Cu alloy composition. In embodiments were the Al—Si—Cu alloy is referred to as comprising one or more alloying elements (e.g., one or more of Si, Cu, Mg, Fe, and Mn) and aluminum as balance, the term “as balance” does not exclude the presence of additional elements not intentionally introduced into the composition of the Al—Si—Cu alloy but nonetheless inherently present in the alloy in relatively small amounts, e.g., as impurities.

In another form, an aluminum alloy composition for manufacturing a three-dimensional high thermal conductivity aluminum alloy part by an additive manufacturing process may comprise, by weight, greater than or equal to 95% aluminum and less than 5% of at least one nucleating agent, and thus may be referred to as a “high-purity Al alloy.” In one specific example, the high-purity Al alloy may comprise, by weight, greater than or equal to 98% aluminum and less than 2% of at least one nucleating agent.

The at least one nucleating agent included in the high-purity Al alloy may comprise an element or compound that exhibits relatively low solid solubility (e.g., less than 1 wt % or, more preferably, less than 0.5 wt %) in aluminum at temperatures less than 530° C. The composition and amount of the at least one nucleating agent included in the high-purity Al alloy may be selected so that the high-purity Al alloy can be heated to a temperature above a liquidus temperature of the high-purity Al alloy and subsequently cooled to a temperature below a solidus temperature of the high-purity Al alloy to produce an entirely solid polycrystalline high-purity Al alloy that predominantly exhibits an equiaxed grain structure, instead of a columnar grain structure.

In particular, the composition and amount of the at least one nucleating agent in the high-purity Al alloy may be selected so that, when the high-purity Al alloy is melted and subsequently cooled from an entirely liquid phase to an entirely solid phase, particles of the at least one nucleating agent will form within a solution of liquid phase aluminum prior to formation of a solid aluminum matrix phase. More specifically, when the high-purity Al alloy is heated to a temperature above the liquidus temperature of the high-purity Al alloy and subsequently cooled to a temperature below the liquidus temperature of the high-purity Al alloy, the high-purity Al alloy will transition from an entirely liquid phase to a multiphase system. During this transition, solid particles of the at least one nucleating agent will nucleate throughout a solution of liquid phase aluminum to produce a multiphase system that includes a solution of liquid phase aluminum and a solid phase of particles of the at least one nucleating agent dispersed throughout the liquid phase aluminum. In the multiphase system, the solid particles of the at least one nucleating agent may exhibit a solubility in liquid aluminum of, by weight, less than or equal to 2%, which may help maximize the number if solid particles within the liquid phase aluminum. Nucleation of the solid particles of the at least one nucleating agent may occur simultaneously throughout multiple horizontally and vertically spaced-apart regions of the solution of liquid phase aluminum, and may occur generally homogeneously throughout the solution of liquid phase aluminum. Thereafter, as the high-purity Al alloy continues to cool, solid phase aluminum dendrites will nucleate and grown in multiple directions on the previously formed nuclei (i.e., on the solid particles of the at least one nucleating agent). Growth of these aluminum dendrites within the solidifying high-purity Al alloy will eventually be arrested when neighboring aluminum dendrites impinge upon one another and form grain boundaries. After the high-purity Al alloy has been cooled to a temperature below the solidus temperature of the high-purity Al alloy and is completely solidified, the high-purity Al alloy will exhibit a polycrystalline structure including a continuous aluminum matrix phase and a dispersed phase of particles of the at least one nucleating agent. In addition, the resulting high-purity Al alloy will predominantly include a plurality of randomly oriented equiaxed grains, instead of columnar grains. The equiaxed grains may have a mean diameter in the range of 0.1 μm to 50 μm.

The high-purity Al alloy may have a liquidus temperature in the range of 660° and 1300° C. and a solidus temperature in the range of 650° and 680° C. As such, the high-purity Al alloy may exhibit a multiphase system of liquid phase aluminum and solid particles of the at least one nucleating agent at a temperature in the range of 650° and 1300° C.

Due to the relatively low solubility of the at least one nucleating agent in solid aluminum, limited amounts of the at least one nucleating agent will be present in solid solution in the aluminum matrix phase after complete solidification of the high-purity Al alloy. As such, inclusion of the at least one nucleating agent in the high-purity Al alloy will have little to no adverse effect on the thermal conductivity of the high-purity Al alloy. For example, after complete solidification, the high-purity Al alloy may exhibit a thermal conductivity in the range of 120 watts per meter-Kelvin (W/(m·K)) to 220 W/(m·K).

In some embodiments, the at least one nucleating agent may comprise an element that, when present in the high-purity Al alloy, exhibits a eutectic point or a peritectic point at a concentration of, by weight, less than 5% of the high-purity Al alloy. In such case, the element may be present in the high-purity Al alloy in an amount that is greater than the amount of the same element in the eutectic or peritectic composition of the Al alloy.

For example, in one form, the at least one nucleating agent may comprise titanium (Ti). A binary Al—Ti alloy exhibits a peritectic point at a composition of, by weight, about 0.12% Ti and a temperature of about 665° C. Therefore, in one form, the high-purity Al alloy may comprise a high-purity Al—Ti alloy including, by weight, greater than or equal to 95% aluminum, greater than 0.12% titanium, and less than 5% titanium. In such case, when this high-purity Al—Ti alloy is melted and subsequently cooled from an entirely liquid phase to an entirely solid phase, solid particles of Al₃Ti will nucleate within a solution of liquid phase aluminum at the liquidus temperature of the alloy. Thereafter, aluminum dendrites will nucleate and grown in all directions on the previously formed Al₃Ti particles, resulting in the formation of a polycrystalline structure that predominantly includes a plurality of randomly oriented equiaxed grains, instead of columnar grains.

Some examples of elements (in addition to Ti) that can be used as the at least one nucleating agent in the high-purity Al alloy include boron (B), beryllium (Be), cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), hafnium (Hf), manganese (Mn), molybdenum (Mo), niobium (Nb), lead (Pb), sulfur (S), zirconium (Zr), antimony (Sb), scandium (Sc), selenium (Se), strontium (Sr), tantalum (Ta), vanadium (V), tungsten (W), and combinations thereof. For example, the high-purity Al alloy may include, by weight, equal to or greater than 0% B to 5% B, 0.7-5% Be, 0.9-5% Co, 0.3-5% Cr, equal to or greater than 0% Cs to 5% Cs, 1.7-5% Fe, 0.4-5% Hf, 1.8-5% Mn, equal to or greater than 0% Mo to 5% Mo, equal to or greater than 0% Nb to 5% Nb, 1.4-5% Pb, equal to or greater than 0% S to 5% S, 0.9-5% Sb, 0.4-5% Sc, equal to or greater than 0% Se to 5% Se, 0.5-5% Sr, equal to or greater than 0% Ta to 5% Ta, 0.12-5% Ti, equal to or greater than 0% V to 5% V, equal to or greater than 0% W to 5% W, and/or equal to or greater than 0% Zr to 5% Zr, and the balance Al.

The high-purity Al alloy may include one or more additional elements that may or may not be intentionally introduced into the composition of the high-purity Al alloy, with such additional elements being present in the high-purity Al alloy in amounts less than 0.2%, preferably less than 0.05%, and more preferably less than 0.01% by weight of the high-purity Al alloy. Additional elements not intentionally introduced into the composition of the high-purity Al alloy may be present, for example, as impurities in the raw materials used to prepare the high-purity Al alloy composition. In embodiments were the high-purity Al alloy is referred to as comprising at least one nucleating agent (e.g., at least one element or compound of Ti, B, Be, Co, Cr, Cs, Fe, Hf, Mn, Mo, Nb, Pb, S, Zr, Sb, Sc, Se, Sr, Ta, V, or W) and aluminum as balance, the term “as balance” does not exclude the presence of additional elements not intentionally introduced into the composition of the high-purity Al alloy but nonetheless inherently present in the alloy in relatively small amounts, e.g., as impurities.

FIG. 2 depicts an apparatus 100 that can be used to manufacture a three-dimensional aluminum alloy part 108 from an aluminum alloy powder feed material 110, which may comprise or consist of the Al—Si—Cu alloy and/or the high-purity Al alloy. The three-dimensional aluminum alloy part 108 may be formed via a powder bed fusion additive manufacturing process, in which digital design data is used to build up the part 108 layer by layer. For example, the apparatus 100 may be configured to manufacture the aluminum alloy part 108 by a powder bed fusion process, which may be carried out using a selective laser melting or an electron beam melting technique. In such case, the apparatus 100 may comprise a building chamber 112 including a building platform 114, a powder feed material reservoir 116 separated from the building chamber 112 by a weir 118, and a high-power energy beam source 120.

A volume of the aluminum alloy powder feed material 110 may be distributed over a surface of the building platform 114, for example, by a blade 122 to form a layer 124 of aluminum alloy powder feed material 110. In one form, the aluminum alloy powder feed material 110 may have a mean particle diameter in the range of 5 micrometers to 100 micrometers and the layer 124 of aluminum alloy powder feed material 110 may have a thickness in the range of 20 micrometers to 100 micrometers. In FIG. 2, the layer 124 of powder feed material 110 is distributed over a surface of the building platform 114 and also over a surface of one or more previously melted, fused, and solidified aluminum alloy layers 126 (FIG. 3). Then, selective regions 128 of the layer 124 are scanned by a high-energy laser or electron beam 130. As shown, the selective regions 128 of the layer 124 scanned by the beam 130 correspond to a cross-section of the three-dimensional aluminum alloy part 108 being formed.

Referring now to FIG. 4, as the high-energy beam 130 scans the selective regions 128 of the layer 124, the beam 130 impinges the layer 124 and heat generated by absorption of energy from the beam 130 initiates melting of the layer 124 within the selective regions 128. As a result, a pool of molten aluminum alloy material 132 is created that fully penetrates the layer 124 and extends through the layer 124 in a direction substantially perpendicular to the surface of the building platform 114 (i.e., along the z-axis). In one form, the pool of molten aluminum alloy material 132 may extend into the layer 124 and partially into the underlying layers 126 at a depth in the range of 10 μm to 300 μm. After termination of the high-energy beam 130, the pool of molten aluminum alloy material 132 rapidly cools and solidifies to form another solidified aluminum alloy layer that bonds with the previously solidified layers 126. For example, after termination of the high-energy beam 130, the pool of molten aluminum alloy material 132 may cool at a rate in the range of 10⁴ Kelvin per second to 10⁶ Kelvin per second. Thereafter, the reservoir 116 may be raised in a build direction (i.e., along the z-axis), or the building platform 114 may be lowered, by a thickness of the newly solidified layer, for example, by a piston 134. Then, a further layer of powder feed material 110 may be distributed over the surface of the building platform 114 and over the previously solidified aluminum alloy layers 126, scanned with the high-energy beam 130 in regions corresponding to another cross-section of the three-dimensional aluminum alloy part 108, and solidified to form yet another solidified aluminum alloy layer that bonds with the previously solidified layers 126. This process is repeated until the entire alloy part 108 is built up layer-by-layer.

In embodiments where the aluminum alloy powder feed material 110 comprises the Al—Si—Cu alloy, the resulting alloy part 108 may be heat treated to dissolve into solid solution any coarse intermetallic phases that may have formed during solidification and/or to promote the formation of one or more Cu-containing precipitate phases (e.g., an AlCu precipitate phase and/or AlCuMgSi precipitate phase) within the aluminum matrix phase. The heat treatment process may include an aging heat treatment stage and optionally a solution heat treatment stage. If performed, the solution heat treatment stage may be performed prior to the aging heat treatment stage. During the optional solution heat treatment stage, the alloy part 108 may be heated to a temperature in the range of 490° C. to 550° C. for a duration of 10 minutes to 10 hours. In one form, the alloy part 108 may be heated during the solution heat treatment stage to a temperature in the range of 490° C. to 550° C. for a duration of 3 hours to 10 hours. In another form, the alloy part 108 may be heated during the solution heat treatment stage to a temperature in the range of 490° C. to 550° C. for a duration of less than 1 hours, for example, for a duration of 10 minutes to 30 minutes. After the optional solution heat treatment stage, the alloy part 108 may be cooled or quenched to a temperature less than 100° C., e.g., ambient temperature, at a cooling rate sufficient to prevent diffusion and precipitation of alloying elements dissolved in into solid solution during the solution heat treatment stage. In the aging heat treatment stage, the alloy part 108 may be heated to a temperature in the range of 180° C. to 210° C. for a duration of 0.5 hours to 7 hours. After the aging heat treatment stage, the alloy part 108 may be cooled or quenched to a temperature less than 100° C., e.g., ambient temperature.

As described in further detail above, the Al—Si—Cu alloy and the high-purity Al alloy each include at least one element or compound that, during solidification of the alloy, nucleates within a solution of liquid phase aluminum and provides sites for the subsequent nucleation and growth of aluminum dendrites. However, referring now to FIGS. 5 and 6, it has been found that, when aluminum alloys that do not include such elements and/or compounds (or do not include appropriate amounts of such elements and/or compounds) are melted and subsequently solidified, columnar-shaped aluminum dendrites 236 tend to grow unidirectionally within the solidifying aluminum alloys and in epitaxy with a surface of an adjacent solid substrate 238 (FIG. 5). As shown in FIG. 6, after solidification, the resulting aluminum alloys exhibit a columnar grain structure including a plurality of unidirectional columnar grains 240. Likewise, it has been found that, when such aluminum alloys are used as a powder feed material in an additive manufacturing process, such as the process described above with respect to FIGS. 2-4, columnar-shaped aluminum dendrites tend to grow unidirectionally in the build direction (i.e., along the z-axis) and in epitaxy with the surface of the building platform 114 or with the surface of one or more previously solidified aluminum alloy layers 126. In addition, this unidirectional epitaxial aluminum dendrite growth tends to persist through each of the subsequently melted and solidified layers of the aluminum alloy part being formed, with the resulting aluminum alloy part being readily susceptible to the formation of cracks along the grain boundaries between the adjacent elongated columnar grains 240.

As shown in FIGS. 7 and 8, when the Al—Si—Cu alloy and the high-purity Al alloy are melted and subsequently cooled, solidification of the alloys begins with the nucleation of solid particles 342 throughout a solution of liquid phase aluminum 344. In the Al—Si—Cu alloy, the solid particles 342 may comprise particles of substantially pure silicon and optionally particles of an Fe- and/or Mn-containing intermetallic phase. Alternatively, in the high-purity Al alloy, the solid particles 342 may comprise an element or compound of Ti, B, Be, Co, Cr, Cs, Fe, Hf, Mn, Mo, Nb, Pb, S, Zr, Sb, Sc, Se, Sr, Ta, and/or V, as described above in further detail. As these alloys continue to solidify, solid phase aluminum dendrites 346 will nucleate and grown in all directions on the solid particles 342, as shown in FIG. 7. Additional aluminum dendrites 347 also may grow in epitaxy with a surface of an adjacent substrate 338. Growth of the aluminum dendrites 346, 347 within the solidifying liquid phase aluminum 344 will eventually be arrested when neighboring aluminum dendrites 346, 347 impinge upon one another and form grain boundaries 348, as shown in FIG. 8. The resulting aluminum alloys will exhibit an equiaxed grain structure including a plurality of randomly oriented equiaxed grains 350. Likewise, when the Al—Si—Cu alloy and/or the high-purity Al alloy are prepared in powder form and used as a powder feed material in an additive manufacturing process, such as the process described above with respect to FIGS. 2-4, aluminum dendrite 346 growth has been found to occur heterogeneously throughout each layer of solidifying aluminum alloy material. In addition, any columnar-shaped aluminum dendrites 347 originating on (e.g., growing in epitaxy with) the surface of the building platform 114 or on the surface of one or more previously solidified aluminum alloy layers 126 are stopped by the aluminum dendrites 346 growing in multiple random directions from the solid particles 342 distributed throughout the bulk of each layer of solidifying aluminum alloy material.

The above description of preferred exemplary embodiments, aspects, and specific examples are merely descriptive in nature; they are not intended to limit the scope of the claims that follow. Each of the terms used in the appended claims should be given its ordinary and customary meaning unless specifically and unambiguously stated otherwise in the specification. 

What is claimed is:
 1. An aluminum alloy powder for manufacturing a three-dimensional high-strength aluminum alloy part by a powder bed fusion additive manufacturing process, each particle of the aluminum alloy powder comprising: an aluminum alloy including, by weight, 13-25% silicon, 0.1-10% copper, and 0-2% magnesium, wherein, when the aluminum alloy is heated to a first temperature greater than a liquidus temperature of the aluminum alloy and subsequently cooled to a second temperature less than the liquidus temperature of the aluminum alloy and greater than a solidus temperature of the aluminum alloy, the aluminum alloy transitions from a liquid phase to a multiphase system, and wherein the multiphase system includes a solution of liquid phase aluminum and a solid phase of silicon particles dispersed throughout the liquid phase aluminum.
 2. The aluminum alloy powder of claim 1 wherein the aluminum alloy comprises, by weight, 15-22% silicon, 2-5.1% copper, and 0.6-0.8% magnesium.
 3. The aluminum alloy powder of claim 1 wherein the aluminum alloy comprises, by weight, 19-21% silicon, 3.5-4.1% copper, and aluminum as balance.
 4. The aluminum alloy powder of claim 1 wherein the aluminum alloy comprises, by weight: greater than 0% iron and less than 9% iron, and greater than 0% manganese and less than 5% manganese, and wherein the multiphase system includes the solution of liquid phase aluminum, the solid phase of silicon particles, and another solid phase of iron-containing intermetallic particles dispersed throughout the liquid phase aluminum.
 5. An aluminum alloy powder for manufacturing a three-dimensional high thermal conductivity aluminum alloy part by a powder bed fusion additive manufacturing process, each particle of the aluminum alloy powder comprising: an aluminum alloy including, by weight: greater than 95% aluminum, and greater than 0% and less than 5% of at least one nucleating agent, and wherein the at least one nucleating agent comprises an element or compound having a solid solubility in aluminum of, by weight, less than 0.5% at temperatures less than 530 degrees Celsius, wherein, when the aluminum alloy is heated to a first temperature greater than a liquidus temperature of the aluminum alloy and subsequently cooled to a second temperature less than the liquidus temperature of the aluminum alloy and greater than a solidus temperature of the aluminum alloy, the alloy transitions from a liquid phase to a multiphase system, and wherein the multiphase system includes a solution of liquid phase aluminum and a solid phase of particles of the at least one nucleating agent dispersed throughout the liquid phase aluminum.
 6. The aluminum alloy powder of claim 5 wherein the at least one nucleating agent comprises an element or compound having a solid solubility in aluminum of, by weight, less than or equal to 2.0% at the second temperature.
 7. A method of manufacturing a three-dimensional aluminum alloy part, the method comprising: (a) providing an aluminum alloy powder feed material; (b) distributing a layer of the powder feed material over a substrate; (c) scanning selective regions of the layer of the powder feed material with a high-energy laser or electron beam to form a pool of molten aluminum alloy material therein, the selective regions of the layer of the powder feed material corresponding to a cross-section of an aluminum alloy part being formed; (d) terminating the laser or electron beam to cool and solidify the pool of molten aluminum alloy material into a solid layer of fused aluminum alloy material; and (e) sequentially repeating steps (b) through (d) to form an aluminum alloy part made up of a plurality of solid layers of fused aluminum alloy material, wherein, during solidification of the pool of molten aluminum alloy material, solid phase particles form within a solution of liquid phase aluminum prior to formation of solid phase aluminum dendrites, and wherein, each of the solid layers of fused aluminum alloy material in the aluminum alloy part includes a continuous aluminum matrix phase that exhibits a polycrystalline structure and predominantly includes a plurality of equiaxed grains.
 8. The method of claim 7 wherein, after termination of the laser or electron beam, the pool of molten aluminum alloy material is cooled at a rate in the range of 10⁴ Kelvin per second to 10⁶ Kelvin per second.
 9. The method of claim 7 wherein, during solidification of the pool of molten aluminum alloy material, the molten aluminum alloy material transitions from an entirely liquid phase to a multiphase system in which the solid phase particles are dispersed throughout the solution of liquid phase aluminum.
 10. The method of claim 7 wherein the solid phase particles serve as nuclei for the subsequent formation of the solid phase aluminum dendrites, and wherein, after the solid phase particles form within the solution of liquid phase aluminum, the solid phase aluminum dendrites nucleate and grow in multiple directions on the solid phase particles.
 11. The method of claim 10 wherein growth of the solid phase aluminum dendrites is arrested when neighboring aluminum dendrites impinge upon one another and form grain boundaries.
 12. The method of claim 7 wherein each particle of the aluminum alloy powder feed material comprises, by weight, 13-25% silicon, and wherein the solid phase particles comprise particles of silicon.
 13. The method of claim 12 wherein each particle of the aluminum alloy powder feed material also comprises, by weight: greater than 0% iron and less than 9% iron, and greater than 0% manganese and less than 5% manganese, and wherein the solid phase particles comprise the particles of silicon and iron-containing intermetallic particles.
 14. The method of claim 12 wherein each particle of the aluminum alloy powder feed material also comprises, by weight, 0.1-10% copper and 0-2% magnesium.
 15. The method of claim 14 including: heating the aluminum alloy part at a temperature in the range of 180° C. to 210° C. for a duration of 0.5 hours to 7 hours to form at least one copper-containing precipitate phase within the aluminum matrix phase of each of the solid layers of fused aluminum alloy material in the aluminum alloy part.
 16. The method of claim 7 wherein each particle of the aluminum alloy powder feed material comprises, by weight: greater than 95% aluminum, and greater than 0% and less than 5% of at least one nucleating agent, and wherein the at least one nucleating agent comprises an element or compound having a solid solubility in aluminum of, by weight, less than 0.5% at temperatures less than 530 degrees Celsius.
 17. The method of claim 16 wherein each particle of the aluminum alloy powder feed material comprises, by weight, greater than 98% aluminum and less than 2% of the at least one nucleating agent.
 18. The method of claim 16 wherein the at least one nucleating agent comprises at least one element or compound of titanium (Ti), boron (B), beryllium (Be), cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), hafnium (Hf), manganese (Mn), molybdenum (Mo), niobium (Nb), lead (Pb), sulfur (S), zirconium (Zr), antimony (Sb), scandium (Sc), selenium (Se), strontium (Sr), tantalum (Ta), vanadium (V), or tungsten (W).
 19. The method of claim 18 wherein each particle of the aluminum alloy powder feed material comprises, by weight, at least one of greater than 0% B and less than 5% B, greater than or equal to 0.7% Be and less than 5% Be, greater than or equal to 0.9% Co and less than 5% Co, greater than or equal to 0.3% Cr and less than 5% Cr, greater than 0% Cs and less than 5% Cs, greater than or equal to 1.7% Fe and less than 5% Fe, greater than or equal to 0.4% Hf and less than 5% Hf, greater than or equal to 1.8% Mn and less than 5% Mn, greater than 0% Mo and less than 5% Mo, greater than 0% Nb and less than 5% Nb, greater than or equal to 1.4% Pb and less than 5% Pb, greater than 0% S and less than 5% S, greater than or equal to 0.9% Sb and less than 5% Sb, greater than or equal to 0.4% Sc and less than 5% Sc, greater than 0% Se and less than 5% Se, greater than or equal to 0.5% Sr and less than 5% Sr, greater than 0% Ta and less than 5% Ta, greater than or equal to 0.12% Ti and less than 5% Ti, greater than 0% V and less than 5% V, greater than 0% W and less than 5% W, or greater than 0% Zr and less than 5% Zr.
 20. The method of claim 18 wherein each particle of the aluminum alloy powder feed material comprises, by weight, greater than 0.12% Ti, less than 5% Ti, and aluminum as balance. 